Here's the situation:
You're about to enter a huge battle. Think "end of Lord of the Rings: Two Towers" kind of battle. What to you yell at the top of your lungs before you join the fray?
By "battle cry", I'm talking about stuff like "For the Horde!", or "By the power of Greyskull!", or if you're feeling sassy "They can take our lives, but they can never take our freedom!". Don't feel the need to steal a quote from someone else, you can make up your own, like say, "For life, liberty, and the pursuit of boobies!". Remember, the battle cry doesn't HAVE to make sense.
I'd probably go with "Leeeeeeroooy Jeeeeenkiiiins!".